For the past 9 years, the Mailman School of Public Health of Columbia University has had an NCI-funded R25T Training Program for cancer investigators in the Population Sciences. Like our longstanding T32 program, the R25 program is a collaboration of faculty, predominantly in Epidemiology, Biostatistics, and Environmental Health Sciences, who have numerous funded cancer-related research projects on which trainees can work. However, the R25 program emphasizes cross-disciplinary training. In addition to taking required and recommended courses in the School of Public Health, R25 trainees rotate through unique individualized modules providing hands-on experience in study design and data collection; behavioral research; laboratory research; health services and outcomes; clinical oncology, and data analysis. Trainees are also required to take courses in cancer biology, research ethics, and research funding; to undertake an in-depth multidisciplinary project with a focus in their specialty; and to make two presentations per year at our weekly multidisciplinary conference. Trainees have the opportunity to attend cancer meetings and meetings in their discipline and are encouraged (but not required) to make presentations at those meetings. Postdoctoral trainees are required to prepare and submit research grant proposals for mock peer review by the faculty. Of the 10 postdoctoral trainees who have graduated from our R25 program, 8 now hold faculty appointments, and 6 of the 8 have NIH K awards. In this competing renewal, we propose to enhance our training in health outcomes/services research, health economics, and the basic biology of cancer; to implement a more detailed evaluation plan; to add to our Advisory Committee, which oversees recruitment, performance and evaluation of the trainees; and to continue consulting with our external advisory committee of 3 outstanding scientist/educators. The R25 has provided support for 5 (1 pre- and 4 postdoctoral) trainees annually. Given our success in postdoctoral training, we now propose to offer R25 traineeships only to holders of a doctoral degree. To maintain the continuity and quality of the program, we have also designated a future successor for the PI.